Hello to the group,
I have been restoring a Hallicrafters SX 140 and it now receives
well and is quite sensitive, but the S meter barely moves. Is this
normal for this receiver or should it move quite a bit like most other
Halli's? Does anyone know if there were any errors on the schematic or
if this radio has any trouble spots? Any hints? 73 Mike KF6KXG

tchrme wrote:
Hello to the group,
I have been restoring a Hallicrafters SX 140 and it now receives
well and is quite sensitive, but the S meter barely moves. Is this
normal for this receiver or should it move quite a bit like most other
Halli's? Does anyone know if there were any errors on the schematic or
if this radio has any trouble spots? Any hints? 73 Mike KF6KXG

Look at the voltage on the AGC line and see. If the AGC voltage is
in the ballpark, there's an issue with the meter or the resistors that
feed it. If the AGC voltage is way off, the receiver may be TOO
sensitive.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

A short while back I posted my findings on an SX-140 resurrection.
You should be able to find it by searching here. Silver mica disease
is all too prevalent nowadays so if thats not an issue for you then
the rest is pretty reliable.
As for the meter...I really haven't paid much attention to it because
its such a cheap bouncy thing but it does seem to read about what I
would expect.

Bill W X 4 A

On Feb 21, 11:30 am, exray wrote:
A short while back I posted my findings on an SX-140 resurrection.
You should be able to find it by searching here. Silver mica disease
is all too prevalent nowadays so if thats not an issue for you then
the rest is pretty reliable.
As for the meter...I really haven't paid much attention to it because
its such a cheap bouncy thing but it does seem to read about what I
would expect.

Bill W X 4 A

Thank you Scott and Bill for your suggestions. After some more time
spent on it, the S meter will read almost full scale when picking up a
nearby sig gen or for the built in crystal calibrator, but barely
moves on other signals. I replaced a tube, most caps, the out of spec
resistors and checked the pots. Could the caps in the IF's be bad if
the audio reception works well but the S meter only work on very
strong signals? I thought the symtom of bad IF caps is thunder crashes
and poor audio. I haven't found anything pulling down the AVC. 73 Mike
KF6KXG

"tchrme" wrote in message
...
On Feb 21, 11:30 am, exray wrote:
A short while back I posted my findings on an SX-140
resurrection.
You should be able to find it by searching here. Silver
mica disease
is all too prevalent nowadays so if thats not an issue
for you then
the rest is pretty reliable.
As for the meter...I really haven't paid much attention
to it because
its such a cheap bouncy thing but it does seem to read
about what I
would expect.

Bill W X 4 A

Thank you Scott and Bill for your suggestions. After some
more time
spent on it, the S meter will read almost full scale when
picking up a
nearby sig gen or for the built in crystal calibrator, but
barely
moves on other signals. I replaced a tube, most caps, the
out of spec
resistors and checked the pots. Could the caps in the IF's
be bad if
the audio reception works well but the S meter only work
on very
strong signals? I thought the symtom of bad IF caps is
thunder crashes
and poor audio. I haven't found anything pulling down the
AVC. 73 Mike
KF6KXG

Bad tuning caps in the IF can cause frequency
instability. The tuning may change from cold to warm. This
is typical of bad mica caps. Bad by-pass or decoupling caps
can cause instability in the form of oscillation, low gain
and other problems. Paper type caps can go bad with age and
should be replaced with more modern ceramic or plastic
types.
I think the mica cap desease mentioned above may be a
rapid instability which shows up as an irregular warbling
where the caps are in the local oscillator. This is
sometimes called scintellation. I am not sure of the cause
but it seems fairly common in silvered-mica types in molded
cases.


--
---
Richard Knoppow
Los Angeles, CA, USA

There's several different bad modes of failing/failed mica caps in the
IF xfmrs. As related to gain as long as the xfmr shows good peaks
during alignment the value should be correct. The thunderstorm noise
and intermittent operation usually occur before the thing goes
completely open.

Are you getting regeneration? I found I could not achieve
regeneration until everything was quite up to par. That seems like a
good measure of its overall health so if there are still problems with
the meter in the AM mode that might be localized to something more
specific than general IF gain.

-Bill

On Feb 23, 1:25 am, exray wrote:
There's several different bad modes of failing/failed mica caps in the
IF xfmrs. As related to gain as long as the xfmr shows good peaks
during alignment the value should be correct. The thunderstorm noise
and intermittent operation usually occur before the thing goes
completely open.

Are you getting regeneration? I found I could not achieve
regeneration until everything was quite up to par. That seems like a
good measure of its overall health so if there are still problems with
the meter in the AM mode that might be localized to something more
specific than general IF gain.

-Bill

Thank you to all who have made suggestions. At this point I have gone
thru every component and all the wiring in the radio (except the IF's
because they peak and I get regeneration and no other symtoms of an IF
problem) and it receives well but while the S- meter moves for the
signal gen signal on AM reception, it only moves a cm at most on
strong received signals. Bringing up the selectivity (regen) to below
oscillation, brings on some more realistic readings, but for the most
part the meter is still not doing its thing. At this point , I am
puzzled esp since it receives so well. Several things I noticed in
going thru it. Someone had replaced a 10K 1watt resistor with a 5.6 K
which I put back to stock. Also they added an electrolytic that is not
on the schematic. I played with it and it is needed to cut some hum.
Since this receiver has had other hands in it, I think a high quality
bottom view picture of the chassis might help me spot something I
missed on the schematic. 73 Mike KF

Since this receiver has had other hands in it, I think a high quality
bottom view picture of the chassis might help me spot something I
missed on the schematic. 73 Mike KF

I can probably help there. I've sent you an email today. If for some
reason it doesn't go thru you may contact me at r a d i o e x r a y at
g m a i l dot com.

-Bill WX4A